This invention relates to a pulse burner incorporated into a water heater or air heater utilized in residences, shops or offices of relatively small size.
In prior art combustion systems, such continuous combustion systems as Bunzen type or Gun type have been used in which gas (usually town gas or propane gas) is burnt continuously with a burner disposed at the lower portion, and the combustion gas is sent to a heat exchanger to heat water or air. In this system, in order to increase the heat efficiency it is necessary to increase the heat transfer area of the heat exchanger or to increase the number or density of combustion gas flow passages. This not only increases the sizes of the heater and fan supplying combustion air but also complicates the mechanism.
In recent years, so called pulse burners have been developed and are disclosed in many publications. In principle, the pulse burner resembles a two cycle gasoline engine, in which fuel and air are sucked into a combustion chamber of a relatively small volume, the mixture is caused to explode by an ignition plug and then exhausted through a heat exchanger in the form of a relatively fine pipe. When explosion occurs, the pressure in the combustion chamber increases greatly thereby to close a flapper valve for stopping suction of the airfuel mixture. Under this condition, the combustion gas is exhausted to the outside of a building via the heat exchanger, thereby creating a negative pressure therein. Then the flapper valve opens automatically to suck again the air-fuel mixture into the combustion chamber. This cycle of operation is repeated at a frequency of 35-80 Hz/sec. The pulse burner has revolutionary advantages over conventional gas or oil burners. More particularly, its heating efficiency is 91 to 96%, meaning saving of fuel and miniaturization of the apparatus, and it does not need a chimney because the combustion product is exhausted at a high speed and high pressure and because the temperature of the exhaust gas is lower than 38.degree. C. Accordingly, an inexpensive plastic pipe (polyvinyl chloride pipe, for example) can be used to extend horizontally to the outdoor through the wall of a building. Without a vertical chimney, heat loss during off cycle is very small. Unexpectedly, the noise cause by frequent explosions is less than 100 dB and can be reduced substantially by suitable means. Moreover, the concentration of the harmful components of the exhaust gas, for example CO, is of the order of less than 0.025% and can be reduced to 0.01-0.005% by volume by suitably selecting the volume of the combustion chamber and the diameter of the exhaust pipe. Irrespective of these advantages, in the prior art pulse burner, the operation of the spark plug and the fan was not satisfactory because of delayed response or miss operation of a flame detector.